Septic shock is a well defined clinical syndrome that is caused by the release of endotoxin or lipopolysaccharide (LPS) by gram negative bacteria. It is known that the endotoxin which is the major antigen which is present in the outer membrane of gram-negative bacteria, is a glycophospholipid which is extremely toxic to mammalian hosts by virtue of its ability to bind, via its toxic moiety Lipid A, on target cells of the immune system such as macrophage and monocytes. The binding results in the massive release of cytokines such as Tumor Necrosis Factor (TNF), Interleukin 1 and 6 (IL-1 and IL-6) as well as gamma Interferon (IFN-gamma), which are the central mediators of LPS-induced shock which can be lethal to the host. The mortality rate in humans due to LPS-induced shock as a consequence of bacterial sepsis, has been estimated in 30-50% of the cases with documented sepsis within 24-48 hours from the onset of the symptoms of the infection. It is also known that endotoxin is a harmful contaminant that has been detected in biologicals and other preparations for parenteral use in humans and animals.
It is known that cationic molecules such as the homologous polymers of basic amino acids, such as, Lysine, have the ability to interact with cell membranes that contain anionic phospholipids. As a result of the interaction between cationic structures and glycophospholipids, one may speculate that homologous polymers of basic (cationic) amino acids might serve as agents to bind and detoxify bacterial LPS. These linear homopolymers of the basic amino acids have the capability of promoting cell to cell fusion and can cause a disruption of the cell membrane of the interacting cells which leads to cell death.
The applicant has discovered that certain peptides which contain the basic amino acid units (homopolymer units) as well as the basic and hydrophobic amino acids (heteropolymer units) according to the formulae: (A).sub.n, (AB).sub.n, and (ABC).sub.n where A is any aliphatic cationic amino acid (at a pH of about 7.0); B and C are any hydrophobic amino acid, both (the aliphatic cationic amino acid and the hydrophobic amino acid) that are characterized by solvent parameter values equal to or greater than +1.5 kcal/mol and -1.5 kcal/mol respectively, will bind to the Lipid A moiety of LPS and will detoxify Lipid A in vitro and in vivo and thus neutralize the effects of endotoxin. The minimal effective peptide sequence to bind Lipid A has been found to be six to seven amino acid residues containing a minimum of three aliphatic cationic amino acids, with a ratio of aliphatic cationic amino acids to hydrophobic amino acids of equal to or greater than 0.5 (R.sub.c/h wherein c is the number of cationic amino acids in the peptide and h is the number of hydrophobic amino acids in the peptide). This ratio is the minimum required for binding Lipid A although high affinity binding of the peptide to Lipid A is reached with sequences of ten amino acids with a ratio (R.sub.c/h) equal to or greater than 1.0.
Accordingly, it is a primary object of the invention to identify peptides that will bind Lipid A.
It is also an object of the invention to provide novel compositions for the treatment or prevention of septic shock which are based on the peptides which have been identified as a class of peptides that are useful in the present invention.
It is also an object of the invention to provide novel methods for the treatment or prevention of septic shock which are based on the use of the peptides which have been identified as a class of peptides that are useful according to the present invention.
It is also an object of this invention to provide novel compositions and methods for the detoxification of biologicals.
These and other objects of the invention will become apparent from the appended specification.